Optical communication techniques, including fiber optics and lasers, are the workhorses of the Internet and high-capacity computing. Meeting the computing and telecommunications needs of the next decades will require advances across a broad front of research and development, including optical signal generation, transmission, switching and routing, as well as intelligent and seamless networking. Although institutions and companies have access to such rapidly growing, high-speed global telecommunication networks, the infrastructure is not yet in place to provide the individual user access that fully exploits the power of light in FO installations.
Known FO diagnostic instruments consist of two expensive categories: 1) long-range units with relatively low resolution for telecommunications and large data networks, where such units generally use optical time domain reflectometery (OTDR) and provide tens of km of span with a resolution of 0.1 to 1 m; and 2) very-high resolution laboratory instruments which utilize optical frequency domain reflectometery (OFDR) providing less than 1 mm resolution.
As used herein, the terms “coherent” or “coherence” mean a uniform wavelength (or frequency). Thus, the term “coherence length” means a distance of air over which the wavelength of laser light is uniform in air.
OFDRs use a tunable wavelength high-coherence laser source. OFDR lasers can provide a wide optical frequency sweep which can translate to very high spatial resolution in a reflectometer, but the cost of the laser source is very high and suppliers are limited. A standard distributed feedback (DFB) laser is much less expensive and can be tuned over a smaller wavelength range, but the DFB laser tunability is sufficient for resolution in the region of 1 cm or less. However, the DFB source does not typically provide sufficient coherence to be used for measurements beyond about 1 m of fiber length.
To support continued large-scale FO deployment, such as in communications networks from homes to data centers, there is an identified need for testing these FO installations at much lower cost, and with high resolution to localize faults in these more compact environments.